Density measurements of a subterranean formation may be based upon exponential law of photon attenuation in the subterranean formation. The photon flux attenuated with distance from the source may depend strongly on the concentration of shell electrons of subterranean formation material (i.e. the electron density). Therefore, by measuring the flux of the photons away from a photon source irradiating the subterranean formation one can extract the so-called subterranean formation electron density. For most materials electron density defines the material mass density by a linear transform.
For photon detection, scintillator-based detectors may be used in density tools for borehole density measurements. The photons entering the crystal produce scintillation light that is amplified and transferred to electronic pulses by photomultiplier tubes (PMTs). These detectors are relatively efficient with increased spectral quality depending on the crystal material. However, the properties of the crystals and the quality and dimensions of PMTs do not always allow the use of such detectors in borehole applications. The crystals and PMTs are relatively fragile and additional shock absorbing packaging is often used for borehole operations. The operating temperature range of many scintillators may also be limited. The PMTs for borehole applications are rather large and may exceed 0.5 inches in outside diameter (OD), and performance generally degrades at relatively high temperatures.